Insulated ducts for electric cables, so-called insulated cable trays, are used in situations where it is important that electric cables should not be damaged in the early stages of a fire, for example in conventional and nuclear power stations or in offshore installations. Such insulated ducts are generally installed in a multiple stage process in which the cables are first attached to a cable tray, which tray is then encased in thermal insulation material and subsequently attached to the installation. Such an installation process is both time-consuming and costly.